1. Field of the Invention
The present invention relates to a process for spacing ATM cells multiplexing several traffic flows of varied profiles and relates also to a device for the implementation thereof.
The invention applies to the management of resources in ATM networks, and more precisely to the "shaping" of the traffic emitted by an ATM source.
2. Discussion of the Background
The source which injects cells into an ATM network may be an ATM user (UNI access, UNI standing for "User Network Interface") or a link-up point between two ATM networks (NNI, standing for "Network Network Interface" or PUNI, standing for "Public User Network Interface").
The sources shape the traffic which they emit under obligation to conform to a compliance contract based on a specific algorithm: the Virtual Spacing Algorithm or GCRA, standing for "Generic Cell Rate Algorithm", a definition of which is given by Recommendation I.371 of the ITU-T (International Telecommunications Union, Telecommunications Section).
With this algorithm it is possible to take two types of traffic profiles into account: traffic at constant bit rate CBR and traffic at variable bit rate VBR. It is based on two parameters: the peak bit rate and the average bit rate.
The peak bit rate is determined by the parameter PCR, standing for "Peak Cell Rate", expressed in cells per second and the average bit rate is determined by the parameters PCR and SCR, standing for "Sustainable Cell Rate", expressed in cells per second, and the parameter MBL, standing for "Maximum Burst Length", expressed in cells defining the maximum length of a burst of cells. The document `A Spacer-Multiplexer for Public UNIs`, P. Boyer & M. Servel, presented during an "ISS'95, World Telecommunications congress" congress, discloses a device which concentrates links emanating from users into a reduced number of high bit rate links directed towards a public network. At the user end, this device polices access and at the network end it carries out the shaping. The shaping function spaces the cells originating from the users with respect to the peak bit rate only. It does not take into account the various qualities of service such as CBR, VBR and UBR, standing for Undefined Bit Rate. The device is output-connected to a single network.
An ATM source multiplexes traffic flows of various kinds. Current solutions do not allow shaping of traffic flows of diverse kinds in order to make them comply with the contract negotiated with a destination network managing a standardized traffic profile. Standardized profiles are the profile with constant bit rate CBR and the profile with variable bit rate VBR.
The purpose of the present invention is to alleviate the aforementioned drawback.